1. Field of The Invention
The present invention relates to a sound field reproducing method of reproducing an arbitrary sound field such as a concert hall, in another space, and also relates to an apparatus for implementing the method. According to the present invention, sound differences due to performance conditions such as directional properties of a sound source such as a musical instrument and the direction of a performer can be reproduced, thereby enabling a sound field to be reproduced with higher presence.
The present application is based on Japanese Patent Application Nos. Hei. 11-230437 and Hei. 11-265966, which are incorporated herein by reference.
2. Description of the Related Art
A related technique of reproducing of an arbitrary sound field such as a concert hall, in a listening room, a laboratory, or the like will be described. As shown in FIG. 2, a sound source S is set on, for example, a stage 12 in a sound field 10 as a concert hall which is to be reproduced, and a sound receiving point R is set in audience seats 14 or the like. As shown in FIG. 3, the space surrounding the sound receiving point R is divided into sound receiving element regions R1, R2, Rj, . . . , and Rm of an appropriate solid angle in which the sound receiving point R is centered. In the example of FIG. 3, the horizontal plane is divided into eight regions, and the obliquely upper area into four regions. In total, the space is divided into twelve regions (m=12). As shown in FIG. 4 (the sound receiving element regions R1 to Rm in FIGS. 4 and 6 diagrammatically show the manner of the division in FIG. 3), an omnidirectional sound source is used as the sound source S. A sound which is radiated from the sound source S, passes through the sound field 10, and then reaches the sound receiving point R is measured by a directional microphone or calculated for each of directions. On the basis of results of the measurements or calculations, an impulse response when the sound radiated from the sound source S passes through the sound field 10, enters one of the sound receiving element regions R1 to Rm, and then reaches the sound receiving point R is obtained for each of the sound receiving element regions R1 to Rm.
FIG. 5 shows the configuration of a system for reproducing the sound field 10 in an arbitrary real space on the basis of the obtained impulse responses hl to hm respectively for the sound receiving element regions R1 to Rm. In an arbitrary real space 16 such as a listening room or a laboratory, loudspeakers SP1 to SPm are placed around a real sound receiving point Rr (usually, a center portion of a plane in the space 16) where a listener or a test subject listens the sound, and in directions corresponding to the sound receiving element regions R1 to Rm (FIG. 3), respectively (in FIG. 5, the positions where the loudspeakers SP1 to SPm are placed are diagrammatically shown in accordance with the manner of showing the sound receiving element regions R1 to Rm in FIG. 4). Right and left or two-channel sound signals which are played back from a sound source apparatus 18 such as a DAT (i.e., Digital Audio Tape recorder) or a CD (i.e., Compact Disc) player are combined into one channel signal and then input into FIR filters (convolution operating units) 20-1 to 20-m via an head amplifier 19. In the FIR filters 20-1 to 20-m, the obtained impulse responses hl to hm are preset as parameters of a convolution operation, respectively. The one-channel sound signal is subjected to a convolution operation in each of the FIR filters 20-1 to 20-m, and sound signals (reflected sound signals) respectively for the directions corresponding to the sound receiving element regions R1 to Rm are produced. The produced sound signals are amplified by amplifiers 22-1 to 22-m, and then played back by the corresponding loudspeakers SP1 to SPm, respectively. The sound signals which are played back in the form of right and left or two-channel sounds from the sound source apparatus 18 are additionally played back as they are as direct sounds at front right and left positions with respect to the sound receiving point Rr. Therefore, the listener at the sound receiving point Rr can enjoy the music in an atmosphere which enables the listener to feel as if the listener is in the audience seats 14 in the sound field 10 of FIG. 2.
In the above, the state where the music performed on the stage 12 of FIG. 2 is listened in the audience seats 14 is reproduced has been described. When a state where the music performed on the stage 12 is listened in real time on the stage 12 is reproduced, it is possible to conduct a rehearsal or the like in an atmosphere which enables a performer to feel as if the performer is in the sound field 10. The reproduction technique will be described. In the sound field 10 of FIG. 2, the sound source S on the stage 12 is set also as the sound receiving point R. The space surrounding the sound receiving point R (=the sound source S) is divided into sound receiving element regions R1 to Rm of an appropriate solid angle in which the sound receiving point R is centered in the same manner as FIG. 3. As shown in FIG. 6, an omnidirectional sound source is used as the sound source S, and a sound which is radiated from the sound source S, passes through the sound field 10, and then reaches the sound receiving point R (=the sound source S) is measured by a directional microphone or calculated for each of directions. On the basis of results of the measurements or calculations, an impulse response when the sound radiated from the sound source S passes through the sound field 10, enters one of the sound receiving element regions R1 to Rm, and then reaches the sound receiving point R is obtained for each of the sound receiving element regions R1 to Rm.
FIG. 7 shows the configuration of a system for reproducing the sound field 10, in an arbitrary real space on the basis of the obtained impulse responses hl to hm respectively for the sound receiving element regions R1 to Rm. In an arbitrary real space 16 such as a listening room or a laboratory, a microphone 24 is placed at a position which is, for example, above that where the performer is to give a performance (the real sound source Sr and the real sound receiving point Rr, usually, a center portion of a plane in the space 16), and loudspeakers SP1 to SPm are placed around the performing position and in directions corresponding to the sound receiving element regions R1 to Rm (FIG. 3), respectively (in FIG. 7, the positions where the loudspeakers SP1 to SPm are placed are diagrammatically shown in accordance with the manner of showing the sound receiving element regions R1 to Rm in FIG. 6). A one-channel sound signal (performance signal) which is picked up by the microphone 24 is input into FIR filters (convolution operating units) 20-1 to 20-m via a head amplifier 19. In the FIR filters 20-1 to 20-m, the obtained impulse responses hl to hm are preset as parameters of a convolution operation, respectively. The one-channel sound signal is subjected to a convolution operation in each of the FIR filters 20-1 to 20-m, and sound signals (reflected sound signals) for the directions corresponding to the sound receiving element regions R1 to Rm are produced. The produced sound signals are amplified by amplifiers 22-1 to 22-m, and then played back by the corresponding loudspeakers SP1 to SPm, respectively. Therefore, the performer at the sound source S and the sound receiving point Rr can conduct a rehearsal in an atmosphere which enables the performer to feel as if the performer is on the stage 12 in the sound field 10 of FIG. 2.
In the sound field reproducing method of the related art, the impulse responses hl to hm respectively for the sound receiving element regions R1 to Rm which are obtained with assuming that the sound source S is omnidirectional are used. In the real sound field 10, however, impulse responses are affected by the directional properties of the sound source S. With respect to a musical instrument of high directionality such as a trumpet, for example, both a listener in the audience seat 14, and a performer feel a large change in audible sensation in cases where the performer on the stage 12 gives a performance with facing toward the audience seats 14, and where the performer gives a performance with facing in a lateral direction with respect to the audience seats 14. In the related sound field reproducing method, even when the performer positioning directly below the microphone 24 turns in the horizontal plane while playing a trumpet, for example, in the system configuration of FIG. 7, the sounds played back from the loudspeakers SP1 to SPm are not changed. In other words, the method cannot reproduce sound differences due to directional properties of a musical instrument or the direction of a performer.
It is an object of the present invention to provide a sound field reproducing method which can solve the problems of the related art and reproduce sound differences due to performance conditions such as directional properties of a sound source such as a musical instrument and the direction of a performer, thereby enabling a sound field to be reproduced with higher presence, and also an apparatus for implementing the method.
To achieve the above object, according to the first aspect of the present invention, there is provided a sound field reproducing method which comprises the steps of dividing a space surrounding a sound source disposed in a sound field which is to be reproduced, into sound source element regions of an appropriate solid angle in which the sound source is centered, dividing a space surrounding a sound receiving point disposed in the sound field, into sound receiving element regions of an appropriate solid angle in which the sound receiving point is centered, calculating or measuring impulse responses, for each of combinations of the sound source element regions and the sound receiving element regions, wherein each of the impulse responses is calculated or measured in the sound field in which a sound radiated from the sound source is emitted from at least one of the sound source element regions, passes through the sound field, enters at least one of the sound receiving element regions, and reaches the sound receiving point, placing a plurality of microphones at positions which surround a real sound source in an arbitrary real space and at an appropriate distance in directions corresponding to the sound source element regions, respectively, placing a plurality of loudspeakers at positions which surround a real sound receiving point in an arbitrary real space and at an appropriate distance in directions corresponding to the sound receiving element regions, respectively, picking up a sound radiated from the real sound source, by the microphones to produce pickup signals, subjecting the pickup signals respectively to convolution operations with the impulse responses which are calculated or measured for the sound source element regions in directions corresponding respectively to the sound radiated from the real sound source, and reproducing respectively sound signals which are obtained by the convolution operations, from the loudspeakers which are placed correspondingly to the sound receiving element regions of corresponding directions, respectively.
Accordingly, when a musical instrument having directionality is played, different sounds are played back depending on the direction of the musical instrument. In a real space in which a performance is to be given, when a performer gives a performance with facing in the direction which corresponds to that on a stage in a sound field to be reproduced, and toward the front of the audience seats, the performance is listened as if the performer gives the performance with facing toward the audience seats, and, when the performer gives a performance with facing in a direction which corresponds to that on the stage and in opposite to the audience seats, the performance is listened as if the performer gives the performance with directing the back toward the audience seats. In this way, sound differences due to performance conditions such as directional properties of a sound source such as a musical instrument and the direction of a performer can be reproduced, thereby enabling a sound field to be reproduced with higher presence.
In the sound field reproducing method of the present invention, a series of operations of the pickups by the microphones, the convolution operations with the impulse responses, and the playbacks by the loudspeakers may be performed, for example, in real time. The signals picked up by the microphones may be once recorded and then played back, and the played back signals may be subjected to the convolution operations with the impulse responses and then played back from the loudspeakers. The sound source and the sound receiving point may be set at the same position in the sound field which is to be reproduced, and the impulse responses may be then obtained. The sound source and the sound receiving point may be set at different positions in the sound field which is to be reproduced, and the impulse responses may be then obtained. The real sound source which gives a performance or the like, and the real sound receiving point where the performance is listened may be set at the same position in the same space. The real sound source which gives a performance or the like, and the real sound receiving point where the performance is listened may be set in different spaces. The manner (the number of regions, and/or the division pattern) of division into the sound source element regions may be identical with that of the sound receiving element regions. When the real sound source which gives a performance or the like, and the real sound receiving point where the performance is listened are set at the same position in the same space, and the manner of division into the sound source element regions is identical with that of the sound receiving element regions, the microphones and the loudspeakers may be respectively paired in accordance with the division manner.
According to the sound field reproducing method of the present invention, for example, impulse responses are obtained while setting the sound source and the sound receiving point at the same position on a stage in a sound field (a concert hall or the like) which is to be reproduced, the microphones and the loudspeakers are placed in a real space (such as a studio or a laboratory) in which a performance is to be given, while setting the real sound source and the real sound receiving point at the same position, and a series of operations of the pickups by the microphones, the convolution operations with impulse responses, and the playbacks by the loudspeakers are performed in real time. Therefore, a performer can conduct a rehearsal in an atmosphere which enables the performer to feel as if the performer is on the stage. For example, impulse responses are obtained while setting the sound source onto a stage in a sound field which is to be reproduced, and the sound receiving point into audience seats, a performance is picked up and recorded while the microphones are placed around the real sound source in the real space in which the performance is given, the recorded performance is played back, convolution operations with corresponding impulse responses are performed, and playbacks from the loudspeakers surrounding the real sound receiving point are performed. Therefore, a performer oneself can check how the performance is listened in the audience seats. For example, impulse responses are obtained while setting the sound source onto a stage in a sound field which is to be reproduced, and the sound receiving point into audience seats, a performance is picked up and recorded while the microphones are placed around the real sound source in the real space in which the performance is given, convolution operations with corresponding impulse responses are performed in real time, and playbacks from the loudspeakers surrounding the real sound receiving point in another real space are performed. Therefore, a live concert in remote places can be performed.
According to the second aspect of the present invention, there is provided sound field reproducing apparatus which comprises a convolution operating unit, in which impulse responses are set as parameters of convolution operations, for each of combinations of sound source element regions and sound receiving element regions, wherein each of the impulse responses is obtained in a sound field which is to be reproduced and in which a space surrounding a sound source disposed in the sound field is divided into the sound source element regions of an appropriate solid angle in which the sound source is centered, a space surrounding a sound receiving point disposed in the sound field is divided into the sound receiving element regions of an appropriate solid angle in which the sound receiving point is centered, and a sound radiated from the sound source is emitted from at least one of the sound source element regions, passes through the sound field, enters at least one of the sound receiving element regions, and reaches the sound receiving point, an adder which additively combines output signals of the convolution operating unit for each of combinations of the corresponding sound receiving element regions, a plurality of microphones placed at positions which surround a real sound source in an arbitrary real space and at an appropriate distance in directions corresponding to the sound source element regions, respectively, and a plurality of loudspeakers placed at positions which surround a real sound receiving point in an arbitrary real space and at an appropriate distance in directions corresponding to the sound receiving element regions, respectively, wherein a sound radiated from the real sound source is picked up by the microphones, pickup signals are subjected to convolution operations by the convolution operating unit with the impulse responses which relate to the sound source element regions of corresponding directions, respectively, and sound signals which are obtained by the convolution operations are additively combined by the adder for each of the sound receiving element regions of corresponding directions, and then reproduced from the loudspeakers which are placed correspondingly with the sound receiving element regions, respectively. Accordingly, it is possible to implement the sound field reproducing method of the present invention. In this case, the sound source and the sound receiving point are set at the same position in the sound field which is to be reproduced, the real sound source and the real sound receiving point are set at the same position in the same space, and a series of operations of the pickups by the microphones, the convolution operations with impulse responses, and the playbacks by the loudspeakers are performed in real time, a performer can conduct a rehearsal in an atmosphere which enables the performer to feel as if the performer is, for example, on the stage.
According to the third aspect of the present invention, there is provided sound field reproducing apparatus which comprises a convolution operating unit, in which impulse responses are set as parameters of convolution operations, for each of combinations of sound source element regions and sound receiving element regions, wherein each of the impulse responses is obtained in a sound field which is to be reproduced and in which a space surrounding a sound source disposed in the sound field is divided into the sound source element regions of an appropriate solid angle in which the sound source is centered, a space surrounding a sound receiving point disposed at a different position in the sound field is divided into the sound receiving element regions of an appropriate solid angle in which the sound receiving point is centered, and a sound radiated from the sound source is emitted from at least one of the sound source element regions, passes through the sound field, enters at least one of the sound receiving element regions, and reaches the sound receiving point, an adder which additively combines output signals of the convolution operating unit for each of combinations of corresponding sound receiving element regions, a plurality of microphones placed at positions which surround a real sound source in an arbitrary real space and at an appropriate distance in directions corresponding to the sound source element regions, respectively, a recording and playing back apparatus which records and plays back signals picked up by the microphones, and a plurality of loudspeakers placed at positions which surround a real sound receiving point in an arbitrary real space and at an appropriate distance in directions corresponding to the sound receiving element regions, respectively, wherein a sound radiated from the real sound source is picked up by the microphones, the picked up sounds are recorded by the recording and playing back apparatus and then played back, the played back pickup signals of the microphones are subjected to the convolution operations by the convolution operating unit with the impulse responses which relate to the sound source element regions of corresponding directions, respectively, and sound signals which are obtained by the convolution operations are additively combined by the adder for each of the sound receiving element regions of corresponding directions, and then played back from the loudspeakers which are placed correspondingly to the sound receiving element regions, respectively. Accordingly, a performer oneself can check how the performance is listened, for example, in the audience seats. In the case where recorded signals which are picked up by microphones placed at positions which surround a real sound source in an arbitrary real space, and which are at an appropriate distance in directions corresponding to the sound source element regions, respectively are prepared, the sound field reproduction may be performed by a playback-only apparatus in place of the recording and playing back apparatus.
According to the fourth aspect of the present invention, there is provided sound field reproducing apparatus which comprises a convolution operating unit, in which impulse responses are set as parameters of convolution operations, for each of combinations of sound source element regions and sound receiving element regions, wherein each of the impulse responses is obtained in a sound field which is to be reproduced and in which a space surrounding a sound source disposed in the sound field is divided into the sound source element regions of an appropriate solid angle in which the sound source is centered, a space surrounding a sound receiving point disposed at a different position in the sound field is divided into the sound receiving element regions of an appropriate solid angle in which the sound receiving point is centered, and a sound radiated from the sound source is emitted from at least one of the sound source element regions, passes through the sound field, enters at least one of the sound receiving element regions, and reaches the sound receiving point, an adder which additively combines output signals of the convolution operating unit for each of combinations of the corresponding sound receiving element regions, a playing back apparatus that plays back signals picked up by a plurality of microphones placed at positions which surround a real sound source in an arbitrary real space, and which are at an appropriate distance in directions corresponding to the sound source element regions, respectively, and a plurality of loudspeakers placed at positions which surround a real sound receiving point in an arbitrary real space, and which are at an appropriate distance in directions corresponding to the sound receiving element regions, respectively, wherein the pickup signals of the microphones which are to be played back by the playing back apparatus are subjected to the convolution operations by the convolution operating unit with the impulse responses which relate to the sound source element regions of corresponding directions, respectively, and sound signals which are obtained by the convolution operations are additively combined by the adder for each of the sound receiving element regions of corresponding directions, and then played back from the loudspeakers which are placed correspondingly with the sound receiving element regions, respectively.